Recently, the number of cylinders in diesel engines of vehicles has been increasing in accordance with demands for higher powers and larger displacement. For example, if a diesel engine has six or eight cylinders, the engine is arranged often as a V type in which the cylinders are arranged in a V shape in order to save space in the engine compartment. As shown in FIG. 4, an intake passage 2 of the V-engine includes a common upstream portion and branched downstream portions, which are connected to a pair of banks 1L, 1R. The intake air is thus distributed to the corresponding cylinders (see, for example, Patent Document 1). An air intake throttle valve 3, which adjusts the intake flow rate, is provided in the upstream portion of the intake passage 2, that is, in the common portion of the banks 1L, 1R. Thus, the amount of the intake air supplied to the banks 1L, 1R is adjusted by the common air intake throttle valve 3 at the same time.
However, if the diesel engine of this configuration has a great displacement, the intake flow rate changes in a wide range. It is thus difficult to accurately adjust the intake flow rate over the wide range using the air intake throttle valve provided commonly for the two banks.
For example, as shown in FIG. 5, intake passages 2L, 2R may be provided separately for the banks 1L, 1R and air intake throttle valves 3L, 3R are arranged in the corresponding intake passages 2L, 2R. This configuration narrows the adjustment range of the intake flow rate for each of the air intake throttle valves 3L, 3R to a half of the adjustment range of the intake flow rate required for the intake flow rate throttle valve provided commonly for the banks. The intake flow rate is thus adjusted accurately.    [Patent Document 1] Japanese Laid-Open Patent Publication No. 2004-124778